Moving coil transducer and enclosure



Feb. 28, 1950 c. L FHQHARDS 2,493,825

Mex/ING com TRANSDUCER AND ENCLOSURE Filed Jan. 19, 1945 atented Feb. 28, Q

UNITED MOVING COIL TRANSDUCER AND EN CLOSURE Claude Langdon Richards, London, England, as-

signor to The Hartford National Bank & Trust Company, Hartford, Conn.

Application January 19, 1945, Serial No. 573,474 In Great Britain September 15, 1943 3 Claims.

rThis invention relates to loudspeakers and microphones of the kind in which a coil carried by a diaphragm is mounted in a magnetic gap, e. g. between pole pieces energized by a permanent magnet.

According to the present invention the magnetic gap is enclosed in a dust and moisture-tight manner in an enclosure one boundary of which is constituted by the diaphragm and which also comprises a movable wall responsive to the pressure variations arising within the enclosure due to the movement of the diaphragm. The movable wall may be constituted by a ilexible sheet of rubber or other flexible material impervious to dust and moisture, the flexible sheet being secured marginally to the rigid framework on which the diaphragm is mounted. Preferably the framework forms a continuous side wall to the enclosure, so that the diaphragm constitutes the front wall and the said movable wall the rear wall.

The use of the movable wall enables the desired sealing against dust and moisture without introducing undesirable damping by confining the enclosed air within a rigid enclosure.

The diaphragm preferably consists of a central conical portion and a flexible surrounding portion constituting the suspension, the coil being mounted at the periphery of the conical portion. The margin of the flexible surrounding portion is clamped to the rigid framework of the loudspeaker between packing rings. The magnet and pole piece system is so designed and is so supported within the enclosed space as to provide air passageways between the space immediately behind the diaphragm and the space immediately in front of the movable wall.

A preferred form of the invention is shown in central section in the accompanying drawing.

The magnet assembly consists of two annular pole pieces I and 2 defining the gap in which the moving coil I3 operates, a permanent magnet 'I (or an equivalent series of bar magnets equally spaced round the pole piece I) and an intermediate member 3 extending between the magnet 4 and the pole piece 2. This magnet assembly is secured in relation to a Cup-shaped casing 5 by means of a number of bolts B each passing through an opening in an external lug 'I on an annular top fixing cap 6 and engaging in an internal lug 9 on a bottom fixing ring I0.

The moving coil I3 which operates in the gap between the pole pieces I, 2 is carried at the periphery of a central conical portion of the diaphragm I2, the flexible surrounding portion forming the suspension being clamped between two packing rings II, which are themselves clamped between an external flange at the upper end of the casing 5 and a shoulder on a top cover cap I4, the edge of which engages behind the flange on the casing 5. The cap I4 is an annulus of large central aperture to give free access to the central conical portion of the diaphragm I2.

At the other end of the casing 5, the' ilexible back I5 is secured between packing rings Il which are clamped-between the ring I0 and a back cover cap I6 the edge of which embraces the ring ID. The cap I5 is spaced from the flexible back I5 by an amount greater than the displacement imparted to the latter by the movement of the diaphragm I2 during normal use. The cap I6, which serves solely for mechanical protection of the `flexible back I5, is apertured or perforated so as to create substantially no air resistance to movement of the ilexible back.

The underside of the diaphragm I2 inside the coil I3 is in direct communication with the flexible back I5 Vby way of an air channel or cavity I9. Similarly the diaphragm I2 outside the coil I3 is in communication with the exible back I5 by way of apertures I8. For a given diaphragm I2 and back I5, the air cavities and apertures I8, I9, may be dimensioned so as to adjust the acoustic performance characteristic. This characteristic may be further modified' by the choice and construction of the back; thus instead of being a flexible sheet of rubber, it could be a diaphragm of the same general nature as the diaphragm I2, or it could be constituted of a central rigid or semi-rigid portion with a flexible surrounding portion, in which case the effect is dependent, among other things, on the mass and stillness of the central portion.

With any given construction of the pressureresponsive back I5 of the enclosure within which the magnet system I-4 is accommodated, the movement of the back I5 may if desired be subjected to frictional damping so as to modify the acoustic performance characteristic.

I claim:

1. An acoustic device comprising, a magnet system including two annular pole pieces concentrically positioned about a common Aaxis so as to form an annular air-gap and a cylindrical center opening, a permanent magnet and an intermediate member magnetically coupled to said pole pieces, a cup like Icasing surrounding the said magnet system, a rigid framework and an external lug, means for securing the said lug and said casing to the said framework so as to securely position the said magnet system to said casing :and said lug, a diaphragm having a central conical portion and -a flexible outside portion, a cylindrically shaped moving coil positioned in the said gap between the said pole pieces and supported at the periphery of the said central conical portion of the said diaphragm, an open top cover cap, packing rings for supporting the said diaphragm adjacent its outer periphery when said top cover is pressed into locking position over the said rings, a flexible disc of dust and moistureproof material having ridge'and valley portions substantially concentric with said conical portion, a perforated bottom cover and packing rings for sealing the said disc to the said casing when the said cover is clamped over the said rings, said diaphragme, said disc, said casing and said rings c-o-acting to form a dust and moisture-proof enclosure for the said system.

2. An acoustic device comprising a magnet system having an annular air-gap therein at one end thereof and an air passageway therethrough from said one end to the opposite end thereof, a diaphragm including a conical central portion and a iiexible outer portion, a coil supported by said diaphragm, said diaphragm being positioned adjacent said one end of said magnet system and facing one end of said passageway and having saidcoil in said air-gap, a flexible wall positioned adjacent said magnet system at said opposite end thereof, said wall facing the other end of said passageway, a cup-shaped casing surrounding said magnet system and having an inturned flange abutting one of said ends thereof, means for clamping said diaphragm to said casing, a rigid ring, means clamping said flexible wall to said ring, a fixing cap abutting the other of said ends of said magnet system, and unitary means for fastening said fixing cap to said casing for clamping said magnet system between said xing cap and said inturned flange and also clamping said ring to said casing whereby a, dust and moisture-proof enclosure for said magnet system is provided that may easily be assembled or disassembled as desired.

3. An acoustic device comprising a magnet system having an annular air-gap therein at one end thereof and an air passageway therethrough from said one end to the opposite end thereof, a diaphragm including a conical central portion and a flexible outer portion, a coil supported by said diaphragm, said diaphragm being positioned :adjacent said one end of said magnet system and facing one end of said passageway and having said coil in said air-gap, a flexible wall positioned adjacent said magnet system at said opposite end thereof, said wall facing the other end of said passageway, a cup-shaped casing surrounding said magnet system and having an inturned flange abutting one of said ends thereof, means for clamping said diaphragm to said casing, a rigid ring, a lug extending therefrom, means clamping said flexible wall to said ring, a fixing cap abutting the other of said ends of said magnet system, a lug extending therefrom and unitary means for fastening said fixing cap to said casing for clamping said magnet system between said xing cap and said inturned flange and also clamping said ring to said casing, said unitary means comprising vscrew means passing through both said lugs and said casing whereby -a dust and moisture-proof enclosure for said magnet system is provided that may easily be assembled or disassembled as desired.

CLAUDE LANGDON RICHARDS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

